On the dilemma between percolation processes and fluctuating pairs as the origin of the enhanced conductivity above the superconducting transition in cuprates

Abstract

The confrontation between percolation processes and superconducting fluctuations to account for the observed enhanced in-plane electrical conductivity above but near T c in cuprates is revisited. This dilemma is currently an open and debated question, whose solution would contribute to the phenomenological understanding of the emergence of superconductivity in these compounds. The cuprates studied here, La1.85Sr0.15CuO4, Bi2Sr2CaCu2O, and Tl2Ba2Ca2Cu3O10, have a different number of superconducting CuO2 (ab)-layers per unit-cell length and different Josephson coupling between them, and are optimally-doped to minimize T c -inhomogeneities. The excellent chemical and structural quality of these optimally-doped samples also contribute to minimize the effect of extrinsic -inhomogeneities, a crucial aspect when analyzing the possible presence of intrinsic percolative processes. Our analyses also cover the so-called high reduced-temperature region, up to the resistivity rounding onset ɛ onset. By using the simplest form of the effective-medium theory, we show that possible emergent percolation processes alone cannot account for the measured enhanced conductivity. In contrast, these measurements can be quantitatively explained using the Gaussian–Ginzburg–Landau (GGL) approach for the effect of superconducting fluctuations in layered superconductors, extended to ɛ onset by including a total energy cutoff, which takes into account the limits imposed by the Heisenberg uncertainty principle to the shrinkage of the superconducting wavefunction. Our present analysis confirms the adequacy of this cutoff, which was introduced heuristically, and that the effective periodicity length is controlled by the relative Josephson coupling between superconducting layers, two long standing debated aspects of the GGL approaches for multilayered superconductors. These conclusions are reinforced by analyzing, as an example, one of the recent works that allegedly discards the superconducting fluctuations scenario while supporting a percolative scenario for the enhanced conductivity above T c in cuprates.